I am trying to rebuild an ios app, that previously had no issues (first rebuild in 6 months or so). Environment is OSX 10.13.5 with all the latest updates, Xcode 9.4.1, Ionic is
You can get this issue if Apple update their terms. Simply log into your dev account and accept any updated terms and you should be good (you will need to goto Xcode -> project->signing and capabilities and retry the certificate check. This should get you going if terms are the issue.